1. Field of the Invention
The present invention relates to an inspection apparatus for inspecting a substrate having irregular concavities and convexities (unevennesses, or protrusions and recesses) used to produce, for example, an organic electroluminescent element, and an inspection method based on the use of the same.
2. Description of the Related Art
An organic electroluminescent element (or referred to as “organic light emitting diode” as well, hereinafter referred to as “organic EL element”) is known as a self-luminescent (self-light emitting) type display element. The organic EL element has higher visibility as compared with the liquid crystal element, and any backlight is unnecessary therefor. Therefore, it is possible to realize the light weight. In view of the above, research and development are vigorously performed in relation to the organic EL element as a next-generation display element.
In the organic EL element, the positive holes introduced from a hole injection layer and the electrons introduced from an electron injection layer are carried to a light emitting layer respectively, they are recombined on organic molecules in the light emitting layer to excite the organic molecules, and thus the light is released thereby. Therefore, in order to use the organic EL element as a display apparatus, it is necessary that the light coming from the light emitting layer should be efficiently extracted or taken out from the element surface. For this purpose, a technique is known as described, for example, in JP2006-236748A, in which a diffraction grating substrate is provided on a light extraction surface of the organic EL element.
In the meantime, the present applicant has disclosed the following method in WO2011/007878A1. That is, a solution, which is obtained by dissolving, in a solvent, a block copolymer that fulfills a predetermined condition, is applied onto a base member, and drying is performed to form a micro phase separation structure of the block copolymer, thereby obtaining a master block (mold) (metal substrate) in which a fine (minute) and irregular concave-convex pattern is formed. According to this method, it is possible to obtain the master block usable for the nano-imprint and the like by using a self-organizing phenomenon of the block copolymer. A mixture of a silicone-based polymer and a curing agent is dropped onto the obtained master block and then cured to obtain a transferred pattern. Then, a glass substrate coated with a curable resin is pressed to (against) the transferred pattern, and the curable resin is cured by irradiation with an ultraviolet light. In this way, a diffraction grating in which the transferred pattern is duplicated is manufactured. It has been confirmed that an organic EL element obtained by stacking a transparent electrode, an organic layer, and a metal electrode on the diffraction grating has sufficiently high light emission efficiency, sufficiently high level of external extraction efficiency, while having sufficiently low wavelength-dependence of light emission, sufficiently low directivity of light emission, and sufficiently high power efficiency.
Even in the case of the organic EL element which uses the diffraction grating produced in accordance with WO2011/007878A1 as described above, when the organic EL element is used as a display device or an illumination device for a mobile phone or a television screen, it is desirable that the light is radiated at a uniform luminance from the entire display surface. Further, it is necessary to avoid the appearance of pattern defect which causes the appearance of intensity fluctuation of light (strong light and weak light) at any minute portion of the display surface. For this reason, it is necessary to confirm the fact that the irradiation from the organic EL element is uniform, i.e., the fact that the luminance unevenness (uneven luminance) is within an allowable range and the fact that the brightness or darkness does not arise at any minute portion, after the completion of the organic EL element. However, if it is judged that the luminance unevenness of the completed organic EL element or the brightness or darkness of the minute portion is without the allowable range, then the organic EL element is regarded as a defective product, and the step of stacking the multiple layers on the diffraction grating as described above becomes wasteful. In particular, the stacking of, for example, the transparent electrode, the organic layer, and the metal electrode is the laborious process in which the production cost is expensive. It is strongly demanded that the defective product as described above is reduced to improve the yield and curtail the wasteful use of the material and the production cost.
In order to evaluate the luminance unevenness, it is necessary that the inspection should be performed simultaneously for a relatively large area. On the contrary, in order to inspect the pattern defect which causes the light intensity fluctuation of the minute portion, the inspection is performed in a relatively narrow field. Further, it is necessary that the former inspection should not be affected by the latter inspection. Therefore, it is necessary that the luminance unevenness and the pattern defect should be inspected and evaluated efficiently and independently. Furthermore, the substrate, which is the inspection objective, is produced by performing the transfer process including, for example, the nano-imprinting. Therefore, it is desirable the luminance unevenness and the pattern defect are also inspected for that the metal mold as the transfer base and the light transmissive mother substrate generated therefrom. For the way of use as described above, it is desirable to adopt an inspection apparatus which can inspect not only the light transmissive substrate but also the light non-transmissive substrate. Moreover, the device, which includes, for example, a sensor for measuring the uniformity of light and the luminance from the display surface having a large area (areal size), is relatively expensive.